The present invention relates to a method for producing water containing ozone by water electrolysis, in detail, the present invention relates to the method and the same apparatus which can produce water containing ozone continually for long time. After here, the term of xe2x80x9cwater containing ozonexe2x80x9d is shown by the tern of xe2x80x9cozone aquaxe2x80x9d.
Conventionally, a gas dissolution method and water electrolysis method are known as typical methods for producing ozone aqua. Recently the water electrolysis method attracts attention, and practical use progresses. The gas dissolution method is a method producing ozone aqua by means of dissolving the ozone gas underwater. The water electrolysis method produces ozone aqua by means of the following process in which oxygen is generated at the side of an anodic electrode, the oxygen is converted to ozone by ozonization catalyst and the ozone is immediately dissolved into water flowing in the anode side. In such a water electrolysis method, a small electrolytic apparatus is employed, which uses water available easily as a material and a s small electric power supply having a specification of Several 10 Volt (V)xc3x97several 10 amperes (A).
As ozone aqua production methods by a water electrolysis, there are inventions proposed by Japanese Patent Laid-Open No. 1-312092, No. 8-134677 and No. 8-134678. Summary of the apparatus will be described on the basis of a typical example shown in FIG. 17. In the FIG. 17, a solid polymer electrolyte membrane 5 disposes between an anode side casing 1 and a cathode side casing 2, which divides the anode side casing 1 and the cathode side casing 2 so as to be an anode chamber 6 and a cathode chamber 7 respectively. The solid polymer electrolyte membrane 5 is merely described with xe2x80x9cmembranexe2x80x9d or xe2x80x9celectrolyte membranexe2x80x9d afterward. An inner surface of the anode side casing 1 is coating with materials having a corrosion resistance as against ozone such as a fluororesin or a glass. In the anode chamber 6 side, an anode 3 is pressed onto and touched with one face of the electrolyte membrane 5, which comprises noble metals 16 such as a platina having catalyst function for generating ozone. On the other hand, in the cathode chamber 7 side, in similar, a cathode electrode 4 is pressed onto and touched with other face of the electrolyte membrane 5, which has a contact face consisting of noble metal 20 such as a platina or silver. Inflow openings 8,9 and outflow openings 10,11 for material water are formed by each of the anode chamber 6 and the cathode chamber 7. DC voltage is applied between both electrodes 3,4 from a direct-current power source 24 through electrode bars 19,23.
In the apparatus having such a constitution, while the water flows through the anode chamber 6 and the cathode chamber 7 respectively, the direct current is applied between both of the electrodes so as to energize. Then water electrolysis occurs across the electrolyte membrane 5. And oxygen and ozone generate in the anode 3 side, hydrogen generates in the cathode 4 side.
The ozone generated the anode 3 side becomes into ozone aqua to dissolve in water, then flows out from the outflow 10 as ozone aqua.
Here, wire nets 16,20 made with the noble metal such as a platina are employed to portions of the both electrodes 3,4 in contact with the electrolyte membrane 5 respectively in order to generate ozone aqua effectively as disclosed by a Japanese Patent Laid-Open No. 8-134677. In addition, on the back face portions of the both electrodes 3,4 in contact with the electrolyte membrane 5, lath nets 17,21 and electrode plates 18,22 are laminated sequentially and joined by mechanical conjugation methods such as a brazing, spot welding, other mechanical conjugation method so as to be integrated. The lath nets 17,21 are made of a materials such as titanium having the corrosion resistance as against ozone. The electrode bars 19,23 are joined with the electrodes having the integrated configuration as described above. While the material water flows through a duct which is formed by wire net and lath net, or lath net and lath net, intense turbulent flow and eddy current arise. By these flow and current, the ozone which arose in the anode side is instantly dissolved into water. Such a dissolution arises in the anode side continuously and then accumulates. As a result, the ozone aqua with high concentration is provided.
By the way, an ability of electrolyte membrane is getting down (membrane fouling) and a concentration of ozone aqua falls as time elapses while the apparatus as described above runs in succession in order to produce ozone aqua of predetermined concentration with an initialized current density. In order to prevent this problem, a method is taken, which raises current density. To describe in detail, as shown in FIG. 18, the current value A is controlled so as to maintain the concentration X of ozone aqua at a predetermined value Xs while keeping the current density uniformity. The current value rises as running time elapses, and finally, reaches a ceiling value Ae at a time t1. The ceiling value Ae is the maximum value which apparatus can permit. In the condition that the current value has reached the ceiling value Ae, the current value cannot increase any longer. Therefore, the concentration X of ozone aqua decreases gradually, then falls in a predetermined threshold value Xe at the time t2. When ozone concentration reaches this threshold value Xe, generally the running of apparatus is stopped. And the deteriorated electrolyte membrane 5 is exchanged after the apparatus is disassembled. However, according to this operational method, reassembling and disassembling of the ozone aqua production apparatus are troublesome and the apparatus operation efficiency becomes down remarkably, so that a cost for producing ozone aqua becomes expensive.
Therefore, one apparatus is proposed by this applicant et al. in Japanese Patent Application No. 9-340188 (Japanese Patent Laid-Open No. 11-172482), wherein the electrolyte membrane 5 recovers easily without dismantling apparatus so as to reduce the complicated exchange work of the electrolyte membrane.
In this apparatus, the electrode bars 19,23 are respectively connected to in the back faces of the anode electrode 3 and the cathode electrode 4 having the lamination type structure as shown in FIG. 19. At this point, this apparatus is the same apparatus as shown in FIG. 17. However, the structure of the apparatus as shown in FIG. 19 is different form one as shown in FIG. 17 at the following point. In the apparatus shown in FIG. 19, the electrode bars 19,23 pass through through-holes 12,13 respectively. The through-holes 12,13 are respectively formed the anode side casing 1 and the cathode side casing 2. And edges of the electrode bars 19,23 are connected to fluid pressure cylinder devices 14,15 respectively. By this, the anodic electrode 3 and the cathode electrode 4 are able to advance and retreat as against the electrolyte membrane 5 respectively.
Operational method of this apparatus is described in the following.
In FIG. 18, when the current value A reaches to the allowed ceiling value Ae and the concentration X of ozone aqua reaches to the predetermined lower limit value Xe, the running apparatus is stopped (the supplies of the electricity and the water are cut off). And the fluid pressure cylinder 14,15 are actuated as shown in FIG. 20. Then both electrodes 3,4 are respectively apart from the electrolyte membrane 5, the pressing force against to the electrolyte membrane 5 is released. And, by means of keeping this condition for a regular time, the electrolyte membrane is recovered. The both electrodes 3,4 advance toward the electrolyte membrane again, and press the electrolyte membrane 5 by the predetermined pressing force. The supplies of the electricity and the running water are started, and the apparatus is started running again. In other words, the electrolyte membrane which has deteriorated as timewise during the apparatus running, is released from the pressing force and recovered. This operating state is shown in FIG. 22 with a time chart. In similar to the case in FIG. 18, the current value A is controlled so that the concentration X of ozone aqua may be maintained at the predetermined concentration Xs and rises as the running time elapses. At the time t1, the current value A has reached to the ceiling value Ae allowed by the apparatus. As the current value cannot rise any more, the supplies of the electricity and the running water to the apparatus are stopped and the running the apparatus stops. Both electrodes 3,4 are respectively kept apart from the electrolyte membrane 5 as shown in FIG. 20. when this condition is maintained for the predetermined time and the time reaches to the time t3, the both electrodes 3,4 advance to again and press the electrolyte membrane 5. The supplies of the electricity and the running water start again. Then, the running apparatus is started again (at the time t3). Afterward, when the current value A reaches to the ceiling value Ae (at the time t4), the running apparatus is similarly stopped and, after the predetermined time elapses, the running apparatus is started again (at time t5). These above operations are repeated. When the predetermined concentration of ozone aqua is not provided even if the stop and re-staring of the running apparatus are repeated, the electrolyte membrane 5 is exchanged.
In the above case, the number of times for exchanging the electrolyte membrane decrease and the life time of the electrolyte membrane improved. therefor the maintenance of the apparatus can be easy. In these points, this method has the advantages in comparison with the prior method. However, as the apparatus must stop frequently, it is impossible to generate ozone aqua continuously. In this point, this method does not solve the conventional problems basically.
Therefore, the applicant proposes a method improving the above described method in the PCT application (PCT/JP98/5576) that insists on a priority based on Japanese Patent Application No. 9-340188. This method uses also the apparatus for producing ozone aqua by electrolysis as shown in FIG. 19 which has the mechanism for making the both electrodes advance or retreat against the electrolyte membrane. However, this method is different from the above-mentioned method.
To describe in detail, the concentration X of ozone aqua is kept at a constant value Xs as shown in a running time chart of FIG. 23, a process raising current value A is the same process as the above-mentioned method. When the current value A reaches to a ceiling value Ae which is a limit value allowed by the apparatus (time t1). A pressing force P of the electrodes for pressing the electrolyte membrane moves from an initial value P1 to the higher value P2 than P1. Consequently, ozone generation rate improves and the current value A necessary to maintain the predetermined ozone aqua concentration decreases. Accordingly, the current value A falls down from the ceiling value Ae to the normal operation value A0. While the running is continued with this condition, the efficiency of the electrolyte membrane deteriorates again. The current value A necessary to maintain the predetermined concentration of ozone aqua increases gradually again. And the necessary current value reaches to the ceiling value Ae again (time t6). At this time point, the force value P for pressing to the electrolyte membrane moves to the higher value P3 than P2. Consequently, the necessary current value A falls down from the ceiling value Ae to the normal operation value A0 again. Then, the current value A necessary to maintain the predetermined concentration of ozone aqua increases gradually again. And the necessary current value reaches to the ceiling value Ae again (time t7). At this time point, in case that the force value for pressing to the electrolyte membrane can increase more, the similar operations are repeated. However, in case that the force value for pressing to the electrolyte membrane reaches to the set ceiling value, the running apparatus is continued with the condition that the current value is the ceiling value Ae. And, when the concentration X of ozone aqua decreases until under the lower limit value Xe (time t8), the running apparatus is stopped. And, the condition that the electrolyte membrane is pressed by the electrodes is released by a similar way to FIG. 20. Then the stress which acts on the electrolyte membrane is released. Consequently, the membrane function is restored. After that, the following either process is done. One following process is that the electrolyte membrane is pressed by the electrodes again with the initial pressing force value P1, and the supplies of the electricity current and the running water are also started again, then the running apparatus is started again. Other following process is that the apparatus is disassembled and the electrolyte membrane is exchanged, then the running of apparatus is started again.
According to this method, even if the necessary current value A reaches to the ceiling value Ae, the necessary current value can falls down by means of making the force P for pressing to the electrolyte membrane by the electrodes increases. Consequently, the running continuation clock time of the apparatus gets longer by leaps and bounds. However, when the pressing force P by the electrodes reaches to the ceiling value, the running apparatus must be stopped and waited for the reactivation of the efficiency of the membrane. In this point, the continuous running which extends over long term is impossible.
Therefore it is for the greatest purpose of the present invention to obtain a long term continuous running in the electrolysis type ozone aqua production method to improve each betterment method more, which is the heart""s desire.
The present invention has been done under such a point of view, and the present invention includes two methods fundamentally. At first, the first method will be shown in the following. A ozone aqua production method uses an ozone aqua production apparatus which comprises an anodic electrode disposed on one side of an electrolyte membrane, which has a catalyst function for generating ozone, a cathode electrode disposed on other side of the electrolyte membrane, the mechanism which enables both or at least one of both electrodes to advance and retreat. In the ozone aqua production method, DC voltage is applied to between the both electrodes in the condition that the both electrodes press against the electrolyte membrane, ozone aqua is generated at the side of anode by means of water electrolysis to supply water onto both sides of the electrolyte membrane, further, a pressing force condition varies with a preset condition in the state that water and electricity are continuously supplied, and then, returns to the initial pressing force condition, the pressing force condition means one that the anodic electrode, the cathode electrode or the both electrodes press against the electrolyte membrane. Thereby, the electrolyte membrane recovers while the ozone aqua is produced.
In this method, the operation for changing the pressing force against the electrolyte membrane can be carried out by means of decreasing or increasing the pressing force from the electrodes or the combination of these.
In addition, a following pattern for changing the pressing force is preferable, which includes keeping a state lower or upper than the preset pressing force for a regular time. Furthermore, this operation can be done by following two ways. In one way, this operation repeats with the predetermined cycle. In other way, this operation is done once or plural times when it is detected that an ability of producing ozone aqua falls down under the predetermined value. It is optional which method is adopted.
Next, the second method is the method having the operation for varying the current or voltage instead of the operation for varying the pressing force. Concretely, in the state of supplying the water and the electricity continuously, the current value or the voltage value of the direct-current power source varies rapidly in accordance with the preset condition. After that, the current or the voltage varies forcibly so as to return to the initial value or the vicinity. Thereby, the electrolyte membrane recovers while producing ozone aqua.
In this method, the following operation for varying the current or voltage forcibly is preferable, wherein the value varies from the initial value of the operation to a range between 0 or a vicinity minimum value of 0 and a maximum value permissible by the apparatus then the states of the minimum value and the maximum permissible value are respectively held for a regular time, after that, the value returns to the initial value or the vicinity of it. In addition, as concerns a frequency of the operation for varying the value forcibly, there is the following case. One case is that this operation repeats by the predetermined cycle. Another case is that, this operation is done once or the plural times when it is detected that the concentration of ozone aqua or the producing ability deteriorates under the predetermined value, such an operation is.
Besides, in the first and second methods, the electrolyte membrane will not be recovered enough even if the operation for varying the pressing force, or the operation for varying the current or voltage forcibly is carried out. In that case, the production of ozone aqua is stopped and the both electrodes are respectively apart from the electrolyte membrane. This state is kept for the predetermined time then the electrolyte membrane recovers. After that, the production of ozone aqua is started again with the predetermined condition about the operating. According to this method, the life time of the electrolyte membrane can be improved all the more.
Furthermore, there is another way. In this method, when the electrolyte membrane will not be recovered enough even if the operation for varying the pressing force or the operation for varying the current or the voltage forcibly is done, the pressing force value of the electrode against the electrolyte membrane moves to the high pressing force value which is set previously. And the production of ozone aqua is continued. According to this method, it is able to produce ozone aqua continuously for a long time by leaps and bounds.